1. Field of Invention
The invention relates to a mounting structure of a semiconductor device (hereinafter referred to as IC) on a circuit substrate. More particularly, the invention relates to a shielding structure to shield against noises generated by ICs mounted on a circuit substrate.
2. Description of Related Art
Portable transmitters or receivers, watches with FM radios, and watch-type individual-selective-calling receivers are known. In such small sized communication apparatus, for example, a conductive plate or film is arranged in a wristband. This arrangement facilitates fitting the apparatus on a wrist of a user. A loop antenna, i.e., an antenna member, is formed with the plate or film when the wristband is positioned around a wrist.
In such a communication apparatus, as schematically shown in FIG. 7, a circuit substrate 7A is included in the apparatus body. An IC 9 is bonded face-down on a front substrate surface 71A. The front substrate surface 71A faces the side opposing the direction where most of or the entire antenna member 4 is positioned. The IC 9 includes, for example, a high-frequency analog IC 9A, for transmission or reception, and a signal-processing digital IC 9B, which is driven by high-frequency driving signals on the order of a few MHz. The circuit substrate 7A includes a copper coated laminate including a glass-epoxy substrate or a phenol resin substrate as a base member 70A. A copper layer on the front surface of the base member 70A forms a surface pattern 72A for connection to terminals 92 of the IC 9.
Through research concerning influence of high-frequency noise to wrist-fitting-type communication apparatus, for example, the inventor has determined that only low receiving sensitivity and transmitting sensitivity can be achieved when a high-frequency analog IC 9A or a signal-processing digital IC 9B is conventionally face-down bonded on the front surface 71A of a conventional circuit substrate 7A ordinarily used. More specifically, high-frequency noise is generated as indicated by arrow D of FIG. 7 from the active surface 90 (i.e., the surface on which the terminals are exposed, the wiring surface, or the device surface) of the IC 9 including the high-frequency analog IC 9A and the signal-processing digital IC 9B. This high-frequency noise passes directly through the circuit substrate 7A and reaches the antenna member 4, thus lowering the sensitivities.
However, there is a strong demand for size reduction in portable wireless equipment such as mobile cellular phones or PHSs, as well as in wrist-fitting-type communication apparatuses. In order to satisfy such a demand for size reduction, some methods have been offered. Such methods include reduction of circuit area by integration of circuits (forming an IC), or high-density mounting of circuit devices. For such high-density mounting, for example, the size of an IC package may be reduced. ICs may be placed directly on a substrate and connected directly to the substrate by wire bonding. Also, face-down bonding may be employed as disclosed in the invention.
In wireless equipment, noise generated from various circuits in the equipment act as jamming signals when reaching a circuit designed to receive weak signals, such as an antenna or a pre-stage part of a receiver circuit. Also, there is a demand for size reduction in apparatuses. However, the influence of such noise is greater when the antenna, the circuit and other components are more closely disposed relative to each other. Therefore, a significant problem is caused relating to improvement of, for example, receiving sensitivity.
In view of the foregoing problem, an object of the invention is to provide an IC mounting structure and a communication apparatus including a circuit substrate and a noise causing IC bonded face-down thereon. Thus, the influence of high-frequency noises from the IC upon the surroundings is removed.
Another object of the invention is to provide a structure for a communication apparatus including such an IC mounting structure, wherein the positional relationship between an IC and an antenna member is optimized. Thus, the influence of high-frequency noises from the active surface of the IC upon an antenna member is prevented and sensitivity is improved.
In the invention, xe2x80x9cface-down bondingxe2x80x9d includes any method employed for surface-to-surface bonding a surface electrode or a wiring lead, previously formed in an IC semiconductor chip, to a wiring electrode formed on a substrate. The arrangement is such that the electrodes are electrically connected to each other. Accordingly, xe2x80x9cface-down bondingxe2x80x9d also includes xe2x80x9cflip-chip bondingxe2x80x9d.
According to the invention, a shielding electrode layer of a circuit substrate opposes the active surface of the IC. The shielding electrode layer is maintained at a predetermined potential. As a result, even if high-frequency noise is generated from the active surface of the IC, such high-frequency noise is attenuated by the shielding electrode layer. As a result, the electromagnetic field leaking to the surroundings is weak. Therefore, for example, a communication apparatus in accordance with the invention, which uses an IC mounting structure, can utilize high sensitivity since high-frequency noises generated from the active surface of the IC cannot reach the antenna member. Additionally, such shielding against high-frequency noises can be completed by exchanging a conventional circuit substrate with a circuit substrate provided with a shielding electrode layer. Therefore, the invention provides both cost saving and size reduction.
In the invention, the shielding electrode layer is preferably formed at least on the entire area opposing the active surface of the IC. A higher noise-shielding effect can be achieved in relationship to the extent of the area in which the shielding electrode layer is formed. In the invention, the circuit substrate is preferably a multilayer substrate with the shielding electrode layer as an inner layer. With such arrangement, the circuit substrate preferably has a through-hole which conductively connects a surface pattern formed on the substrate surface with the shielding electrode layer. The shielding electrode layer is maintained at the predetermined potential due to the through-hole and the surface pattern. The surface of the circuit substrate has a surface pattern which is necessarily maintained at a potential of a ground or a power supply. As a result, if the surface pattern is conductively connected to the shielding electrode layer through the through-hole, the shielding electrode layer can be maintained at a predetermined potential, i.e., the potential of the ground or a power supply, without additional supply of electricity.
Such a mounting structure of a semiconductor device can be used for enhancing sensitivity of a communication apparatus, for example. In this case, the IC generating high-frequency noises is a high-frequency analog IC which includes at least a transmitting function or a receiving function, a signal-processing digital IC driven by high-frequency driving signals, or an IC of a CPU, for example.
In the invention the IC which generates high-frequency noises is preferably face-down bonded on the circuit substrate such that the active surface faces the side opposing the direction in which most or all of the antenna member is positioned relative to the circuit substrate. According to such arrangement, even if a high-frequency noise generated from the active surface of the IC leaks, the noise will rarely reach the antenna member. Thus, sensitivity of the communication apparatus can be further improved.
In the invention, the communication apparatus may be of a type which fits around the wrist of a user, i.e., wrist-fitting. Further, the body of the apparatus preferably has a front surface that includes a display area. The apparatus further includes a wristband which extends from the apparatus body to the back surface and facilitates fitting the apparatus body on a wrist. The antenna member is formed in the wristband.